Most of the power used by modern hard disk drives is consumed by the spindle motor. When the hard disk is initially started up, the motor may draw a peak level of power that is more than two times what it takes to keep the disk spinning. While in most cases even the peak start-up power usage is not substantial, there may be an issue when using multiple hard disks that attempt to spin-up simultaneously. Such an occurrence requires a sufficient power supply to withstand this initial demand.
As a solution to the above-described problem, staggered spin-up is implemented in systems where the host system may spin up the disk drives sequentially. Staggered spin-up significantly lowers design requirements and the cost of the power supply, and avoids overloading of the power supply, reducing the risk of damage to the power supply and the disk drives.
In Serial ATA II; extensions to Serial ATA 1.0a, pin 11 of a power segment of a device connector may be used to control whether staggered spin-up should be used on a particular device. When pin 11 is asserted, the device is allowed to spin up immediately after power on. The host can drive pin 11 low to disable staggered spin-up.